1. Field of the Invention
This invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile, etc., in which an electrostatic photographic technology is employed.
2. Description of the Prior Art
An image forming apparatus is widely used which performs the following process. A photosensitive layer of the surface of an image carrier member is uniformly charged by a charging member. Optical image information is then supplied to the image carrier member in order to produce an electrostatic latent image. Thereafter, a toner, which is usually held in a powder-like state, is supplied to the electrostatic latent image in order to make the latent image visible, and then the toner image is electrostatically transferred to a sheet-like transfer member such as paper. This sequence of procedures are repeated as often as required.
As photoconductive materials of the photosensitive layer of the image carrier member of the image forming apparatus, use is made of selenium, cadmium oxide, zinc oxide, etc., which are each an inorganic photoconductive material. Besides those materials, recently, a wide variety of organic compounds have been employed.
As examples of those organic compounds, use is made of an organic photoconductive polymer (e.g., poly-N-vinylcarbazole and polyvinylanthracene), a low molecular organic photoconductive material (e.g., carbazole, anthracene, pyrazolines, oxadiazoles, hydrazones, and polyarylalkanes), organic dyes (e.g., cyanide dye, indigo dye, thioindigo dye, and squaric acid methane), or organic pigment (e.g. phthalocyanine pigment, azo pigment, polycyclicquinone pigment, and perylene segment).
Since these substances are easy to compose compared with the afore-mentioned inorganic photoconductive materials and tend to form ones which exhibit photoconducting in an appropriate wavelength band, they are used more frequently. For example, U.S. Pat. Nos. 4,123,270, 4,251,613, 4,251,624, 4,256,821, 4,260,672, 4,268,596, 4,278,747, 4,293,628, etc. disclose an image forming apparatus in which an azo pigment exhibiting photoconductive properties is utilized for an image carrier member as an electric charge generating layer in a photosensitive layer which is divided into the electric charge generating layer and an electric charge transporting layer according to functions.
In an image forming process utilizing such an image carrier member, there is, in many cases, employed a corons discharge type charging member as means for charging the image carrier member, in which the image carrier member is charged by corona generated by applying a high D.C. voltage of about 5 to 8 kv to a metal wire of a charge device.
However, in a charging member of this type, ozone and nitrogen oxides are generated when corons discharge is made. The generation of ozone and nitrogen oxides often gives damage to the carrier member itself. Also, those ozone and nitrogen oxides can be a cause of image deterioration by being stuck to the image carrier member. Moreover, this type of charging member has another problem in that the amount of the discharged current flowing toward the image carrier member is so small as about 5% to 30% and thus inefficient.
In order to obviate the above-mentioned drawbacks, a contact-to-charge type charging member is proposed which is designed such that the charging member is directly contacted with an image carrier member. According to this type of charging member, the charging member in the form of a roller, a belt, a blade, or the like is brought into contact with the surface of the image carrier member, and then a D.C. voltage or a voltage in which an alternating current is superimposed on a direct current is applied to the charging member to charge the image carrier member.
The above-mentioned contact-to-charge type charging member has advantages in that there is no generation of ozone and nitrogen oxides and voltage can efficiently be applied to the image carrier member. On the other hand, it has disadvantages in that since the charging member is in contact with the image carrier member, foreign matters, such as toner and paper powder, are readily stuck to the charging member, thus causing image deterioration.
In view of the above, Japanese Laid-Open Patent Application No. Hei 2-272589 discloses a construction in which a cleaning member made of a felt material is brought into contact with a charging member so that the surface of the charging member is cleaned by the cleaning member.
However, in the image forming apparatus disclosed in the above publication, since the cleaning member with respect to the charging member is selected in view of a kind of material, cleaning effect of the cleaning member on the charging member is significantly fluctuated depending on roughness of the surface of the charging member and the particle diameter of the toner powder stuck to the charging member.
Furthermore, the cleaning effect on the charging member is also significantly fluctuated depending on the relationship between roughness of the surface of the charging member and the thickness of fibers constituting the cleaning member.
The inventors of the present application have studied hard paying attention to those points mentioned above and finally accomplished the present invention.
It is therefore a first object of the present invention to efficiently remove the toner powder stuck to the surface of a contact charging member by means of a cleaning member in the light of a relationship between roughness of the surface of the contact charging member and the particle diameter of the toner powder stuck to the surface of the contact charging member.
A second object of the present invention is to efficiently remove the toner powder stuck to a contact charging member in the light of a relationship between roughness of the surface of the contact charging member and the thickness of fibers constituting a cleaning member.
A third object of the present invention is to achieve the first and second objects at a low cost.